Formaldehyde is a common indoor pollutant existing in homes, offices, public buildings, etc. It is a highly reactive chemical and can cause health problems such as headache, dizziness, nausea, and irritations of the eyes, respiratory passages and skin. A major source of formaldehyde emissions is the building materials such as plywood, particleboard, paneling, laminates, carpet glues, and wallpaper containing urea-formaldehyde adhesives. Examples of other sources of formaldehyde include foam insulation materials, paints, and coatings in which formaldehyde-based resins are present. The formaldehyde gas emissions may result from the presence of unreacted formaldehyde in the resins or from degradation of the cured resins.
Various technologies have been cited in the prior art for the purpose of removing airborne formaldehyde. U.S. Pat. No. 5,352,274 discloses air filtration utilizing a plurality of corrugated base sheets which are stacked or nestled and which have entrapped carbon dust for adsorption of impurities such as formaldehyde, acetaldehyde, and acrolein. The corrugated structure provides very little pressure drop as the air passes through available channels and large, powerful fans are not necessary to move air therethrough. This technology provides a method to adsorb formaldehyde molecules physically but not by chemically reaction.
U.S. Pat. No. 5,830,414 discloses an air cleaning filter comprising activated carbon fibers in the form of a web supporting at least one kind of chemical reagent selected from the group consisting of (a) an alkali agent selected from a hydroxide or carbonate of an alkali metal, (b) an acidifying agent selected from acid aluminum phosphate or phosphoric acid, and (c) an oxidizing agent composed of active manganese dioxide resulting from an alkali permanganate and an alkali iodate. This patent discloses the treatment of carbon fibers with an active small molecule such as a strong acid, strong base, or strong oxidizing agent. These chemicals can only be used to treat fibers having high chemical resistances such as activated carbon fibers. Further, fibers thus treated are potentially hazardous to handle.
U.S. Pat. No. 4,517,111 provides a composition comprising a permanganate salt adsorbed onto a solid alkaline support useful for irreversible removing formaldehyde from air. The composition can be employed in molded, pellet, particle, or power form as, for example, in a respirator filter cartridge. The application of this technology is limited to the solid forms as stated. U.S. Pat. No. 4,892,719 discloses a method of reducing the indoor air concentration of aldehydes by coating a porous support filter with a water soluble polymeric amine such as polyethyleneimine, polyallylamine, or polyvinylamine. The coating is further plasticized with a low volatile liquid such as glycerol in order to extend the useful life of the coating. This technology has a deficiency in that the reactive component, i.e., an amine, may be consumed by carbon dioxide present in air. The description of the reaction of carbon dioxide with amine adsorbents may be found in Int. J. Environmental Technology and Management, Vol. 4, Nos 1/2, 2004, p. 82. Furthermore, the reaction product of said polyamine and formaldehyde has the same end group as has urea-formaldehyde and, as a result, over time will undergo the same degradation to release formaldehyde.
It is known that compounds having active methylene groups are capable of reacting with formaldehyde. JP 57,032,729 describes a method for removal of residual formaldehyde in microcapsule dispersion by adding a compound having an active methylene group such as methyl acetoacetate, ethyl acetoacetate, or diethyl malonate. Active methylene compounds also have been used as formaldehyde scavengers in the textile industry to reduce the amount of formaldehyde released from durable press-treated fabrics as described in Textile Chemist and Colorist, Vol. 16, No. 12, p. 33, December 1984 (published by the American Association of Textile Chemists and Colorists). Such a compound is added to finishing formulations of the fabrics to react with formaldehyde released from urea-formaldehyde resins used for cellulose crosslinking. Dimethyl 1,3-acetonedicarboxylate having two highly activated methylene groups was found to be most effective.
U.S. Pat. No. 5,160,503 discloses a water-soluble blend composition for scavenging formaldehyde in textile fabrics. The composition consists of a substituted or unsubstituted polyhydric alcohol such as diethylene glycol and an active methylene compound selected from the group consisting of dialkyl malonates and alkyl acetoacetates. U.S. Pat. Nos. 5,194,674; 5,268,502; and 5,446,195 disclose that water-soluble compositions prepared by reacting a glycol or polyether with an acetoacetate or malonate may be used as formaldehyde scavengers in the fabric finishing formulations. Again, in these references, liquid reaction media are required for the effective removal of formaldehyde.
Formaldehyde scavengers containing active methylene hydrogens also may be added to coating compositions containing urea/formaldehyde or melamine/formaldehyde resin to reduce formaldehyde concentration. U.S. Pat. No. 5,795,933 discloses a waterborne coating compositions comprising a formaldehyde-containing resin and a formaldehyde scavenger containing active methylene hydrogen with a pKa of about 5 to 13.
The reaction of acetoacetate-functional polymers with formaldehyde also has been cited in the prior art. JP 58,059,263 describes a curable polymer composition consisting of a water soluble polymer, a water soluble polymer having an acetoacetate group such as acetoacetylated polyvinyl alcohol resin, and a crosslinking agent capable of reacting with the acetoacetate group such as formaldehyde or glyoxal. U.S. Pat. No. 5,767,199 discloses an air-curing composition containing an acetoacetate functional polymer and an end-blocked polyformaldehyde chain. According to the patent, the composition is stable to reaction until the formaldehyde is released from the polyformaldehyde chain. These references relate to either the utilization of active methylene compounds to remove formaldehyde in a liquid mixture or to suppress formaldehyde emission by mixing a formaldehyde scavenger with formaldehyde-containing resins. None of the references pertain to air filter applications.
Cigarette smoke resulting from tobacco combustion contains numerous gaseous and particulates compounds. The gaseous molecules are responsible for both the pleasure and the health risk derived from the use of tobacco smoke. Among the many molecules produced by combustion or vaporization of tobacco are nicotine, carbon monoxide, ammonia, aldehydes such as formaldehyde, acetaldehyde, and acrolein, and added flavor compounds and combustion products thereof. Cigarette filters are utilized in an effort to remove undesirable gases and particulates from tobacco smoke while retaining the flavor and taste essential to the enjoyment of smoking. Selective removal of gaseous molecules from tobacco smoke is required for an effective active, tobacco smoke filtration material. Active materials such as activated carbon, silica gel, alumina, and zeolites commonly used for the removal of gaseous contaminates are not particularly suitable for this purpose. Although these materials can remove certain gaseous compounds, they also may adsorb compounds considered desirable for acceptable cigarette flavor. Moreover, adsorption by these porous materials is not totally effective since the gaseous compounds are only physically bound to the surface of the porous materials and are not chemically reacted. In addition to selective adsorption of gaseous compounds, active tobacco smoke filter materials also should be light weight, low cost, stable in air, exhibit low pressure drop, safe to handle, and ease of fabrication.
U.S. Pat. No. 6,595,218 discloses a tobacco smoke filter comprising a reagent consisting essentially aminoethylaminopropylsilyl silica gel or aminoethylaminoethyl-(aminopropyl)silyl silica gel wherein the reagent chemically reacts with and removes a gaseous component such as an aldehydes from tobacco smoke. U.S. Pat. No. 6,481,442 discloses a smoking article comprising a wrapper and a selective filter element having at least one carrier and a polyaniline having a plurality of moieties selected from the group consisting of an amino group, an imino group, a hydrazide group, a hydrazone group, a semicarbazide group and combinations thereof capable of reacting with carbonyl-containing combustion products of tobacco. Optionally, a spacer, having the composition —CO—[CH2]n—CO—, wherein n has a value from 1 to 4 or greater than 4, may be used to attach active moieties containing amino groups to the carrier. The spacer is used for the purpose of extending out the chemically active amino moieties from the carrier.
U.S. Pat. No. 4,182,743 discloses a gas-permeable substrate, particularly adapted for the selective removal of aldehydes form gases comprising a granular-containing concentrated hydrogen peroxide, water and a hydrophilic stabilizer for the hydrogen peroxide. U.S. Pat. No. 4,753,250 discloses a process for producing cigarette filters comprising a compound containing L-ascorbic acid to react with and remove aldehydes. U.S. Pat. No. Re. 28,858 discloses an improved tobacco smoke filter material comprising a porous particulate carrier impregnated with polyethylene-imine for the removal of volatile smoke acids and aldehydes. U.S. Pat. No. 5,009,239 also relates to the removal of aldehydes using polyethyleneimine as the active component in a cigarette filter. For the same purpose, an aminobenzene acid salt is used in U.S. Pat. No. 5,603,927 and an organic salt of mercapto-alkane-sulfonate used in U.S. Pat. No. 4,532,947. Disclosed in U.S. Pat. No. 5,206,204 is an adsorbent for lower aldehydes which comprises a saturated cyclic secondary amine and a halogenide of an alkali metal or alkaline earth metal supported on a porous carrier.
A tobacco smoke filter comprising a plasticizer bonding agent is disclosed in U.S. Pat. No. 3,227,164, wherein the plasticizer is selected from the group consisting of the alkylene glycol, polyalkylene glycol, and glycerol esters of acetoacetic acid. This reference discloses that the tobacco smoke filter is effective in removing phenol and undesirable toxic metal ions such as nickel, cobalt, etc. Aldehydes removal is not mentioned.